Not sure, but I do know that a feather weight filler is made. I just got a gallon of it for the front fenders that my friend is working on. After sanding, it should narrow down to just a dusting on the metal. A true body man will smudge on a good amount and sand it all off leaving small skim coats. The lead might have been because of the paint not being an issue where as maybe the vinyl can react differently with bondo.
